The invention relates generally to quality function deployment (QFD) and in particular to a method of quality function deployment which preserves the system architecture. A system can be represented as an assemblage of elements working in tandem and forming a unitary object that performs one or more tasks. Typically, components of a system cannot meet the objectives assigned to the whole system. Therefore, a system may be described by its elements, their merits, and the relationships that tie them together. In addition, a component of a system can itself be a system. For example, an engine is a component of another system, an airplane, which in turn can be a part of a bigger system, air transportation, and so on. A tree structure of system, sub-systems, components, parts, etc. can be utilized to represent a system. FIG. 1 shows an exemplary architecture of a projector system which includes sub-system and component levels.
The ability of the system to meet its assigned objective can be gauged using certain figures of merit or critical to quality (CTQ) parameters. Similarly, each element of the system has its own list of CTQ""s upon which the performance of the element as part of the system can be gauged. The values of the CTQ""s at a first level (e.g., the system level) may depend on the values of the CTQ""s at subsequent levels (e.g. sub-system and component levels).
Methods have been developed to define CTQ""s at various system levels so that the overall system CTQ""s can be met. Quality Function Deployment (QFD) is a known process for identifying CTQ""s and flowing them down to subsequent levels. FIG. 2 is a block diagram of a CTQ flow down process. The relationship between each level CTQ""s and key control parameters (KCP""s) has been referred to as a house of quality. FIG. 2 shows the flow of CTQ""s from the customer requirements to functional requirements and then to part characteristics down to manufacturing processes CTQ""s and to process variables. At each level, the CTQ""s are identified and their relations to the higher level CTQ""s are specified qualitatively by high (designated h), medium (designated m), or low (designated l), depending on the relation strength. FIG. 3 is an exemplary house of quality or quality matrix relating customer expectations represented by CTQ""s 2 to product requirements represented by key control parameters 4 (KCP""s). FIG. 3 illustrates the qualitative effect that each KCP 4 has on one or more CTQ""s 2.
When applied at the system level of the example in FIG. 1, QFD will yield a first house of quality for that system as shown in FIG. 3. In that house of quality, KCP""s 4 corresponding to different sub-systems of the overall system (e.g. lamp, cooling, lens) are not arranged in any order. This results in a loss of the system architecture and renders analysis of sub-system and component requirements difficult. The problem is particularly evident when flowing down the CTQ""s to components and parts of each subsystem. If the tree structure in FIG. 1 is deep, the CTQ list will grow in size and the system structure will be difficult, if not impossible, to ascertain. Therefore, existing QFD is valuable for xe2x80x9cshallowxe2x80x9d systems (e.g., systems with a limited number of elements and levels) but has disadvantages when applied to xe2x80x9cdeepxe2x80x9d systems having numerous levels and components.
An exemplary embodiment of the invention is directed to a method for performing quality function deployment for a system having a plurality of levels. The method includes obtaining a plurality of first level critical to quality parameters and obtaining a plurality of first level key control parameters. A first level quality matrix is generated identifying an effect at least one first level key control parameter has on at least one first level critical to quality parameter. The first level key control parameters are arranged into a first group and a second group. A second level quality matrix is generated for the first group. The second level quality matrix includes second level critical to quality parameters corresponding to the first group of first level key control parameters and at least one second level key control parameter. The second level quality matrix identifies an effect at least one second level key control parameter has on at least one second level critical to quality parameter.